Hi Valerie,
I'm fairly new to Buenos Aires as well--a whole month so far. I could give you a few tips based on my experiences so far (and what I've heard from others) but like Claudine says, it depends on what you're interested in. Art, music, sports, night life, food, etc...?
I'm here until the end of July, so I'd be happy to meet up and explore more of the city.
Take care,
Kristen.